The present invention relates to glass products and a process for making the same wherein the glass products, and in particular, fiberglass filaments, exhibit an enhanced resistance to corrosion by cement liquors. The glass products are thereby rendered suitable for the production of composite materials containing cement and/or concrete.
It has been known that cement, mortar, and concrete materials have a low resistance to tension, bending, and impact stresses, but said resistance can be considerably increased by the addition, for example, of fiberglass filaments. This is particularly true when the glass filaments are introduced into the cement in the form of organized skeins of thread, or as cut threads whose filaments are arranged parallel to each other rather than in the form of snarled wool. In large scale technical production, such continuous filaments are predominantly made of E-glass.
It has been found, however, that glass filaments, e.g., E-glass filaments, become highly corroded when incorporated into Portland cement and other cementitious products due to the high alkalinity of said cement thereby causing the strengthening effect of the filaments to become completely lost. This alkali attack and subsequent fiber strength loss generally so weakens the fibers that long term reinforcement of a cement matrix by glass fibers, e.g., E-glass fibers, is neither predictable nor dependable.
In order to increase the resistance of fiberglass filaments to corrosion, several methods have been used in the prior art including (1) the coating of the fiberglass filaments with plastics; and (2) the use of highly alkaline-resistant types of glass filaments. The first method is not satisfactory because of its poor adhesion to a cement matrix as well as the difficulty of producing a lasting, dense coating on said glass filaments.
With respect to the alkali-resistant glasses, e.g., the Na.sub.2 O-ZrO.sub.2 -SiO.sub.2 -system, they are much less corroded than E-glass, but their destruction is merely delayed. The alkali-resistant glasses further have the disadvantage in that they are considerably more difficult to melt and extrude into filaments than E-glass.